Non-rotating, levitating, cylindrical air-pillow method for supporting and guiding an endless flexible casting belt into the entrance of a continuous metal-casting machine

ABSTRACT

Non-rotating, belt-levitating, cylindrical air-pillow apparatus and method supporting and guiding a moving, tensed, flexible, heat-conductive casting belt along a convex, cylindrically shaped path toward an entrance into a continuous casting machine. Pressurized air is applied in belt-levitating relation to the inner surface of the casting belt moving along the path. Stationary belt-guiding elements define the path. Pressurized air is fed through throttling passages communicating with regions between stationary elements or communicating with outwardly facing stationary plateau surfaces. The pressure level of belt-levitating air is at least about 90% but not exceeding 100% of a pressure level which lifts the casting belt away from contact with the stationary elements. For reducing flexural stress in the belt moving toward the entrance, a radius of curvature R1 of the cylindrically shaped path is progressively reduced by employing variable radius R+ progressively increasing in a direction toward the entrance. Pressurized air is allowed to escape from its belt-levitating relation, but escape is restricted by a semi-seal throttling barrier extending along a perimeter of the belt path. An outer surface of the barrier has fine grooves for distributing escaping pressurized air thereover. A cylindrical shell supports the stationary elements and is adjacent to a plenum chamber feeding pressurized air through throttling passages in the shell. Stationary elements of suitable, durable, wear-resistant, slippery material are mounted in grooves in the shell. Air-pillow apparatus includes belt coolant application deflector or nozzles.

[0001] FIELD OF THE INVENTION

[0002] This invention is in the field of continuous metal-castingmachines having a substantially straight or flat moving mold cavity ormold space wherein a casting belt or belts travel from an entrance intoand along the mold space to an exit therefrom. The term “substantiallyflat” herein includes such gentle longitudinal curvature as may assistin keeping a single tensed travelling casting belt against backup meansin the moving mold casting space and also includes such gentletransverse curvature as may assist in keeping the belt in firm contactwith the surface of metal being solidified in the moving mold space.

BACKGROUND

[0003] Casting belts in continuous casting machines for continuouslycasting molten metal are formed of suitable heat-conductive, flexiblemetallic material as known in the art, having a thickness for example ina range from about 0.3 millimeters to about 2 millimeters. Such a beltis revolved under high tensile forces around a belt carriage in an ovalpath. During revolving, each belt has, in the prior art, continuouslypassed around a rotating entrance-pulley drum and a rotating exit-pulleydrum positioned respectively at entrance and exit ends of the movingmold.

[0004] A persistent problem in the use of such machines has been aspatial limitation alongside the inner surface of the casting belt nearan entrance region of the casting space where molten metal firstcontacts the belt as the belt separates from the rotating entrancepulley drum. In the prior art as disclosed in patents of Hazelett etal., referenced above, this spatial limitation can be seen in a sideelevation view. This limitation occurs in the form (shape) of a cuspdefined between a belt's inner surface and a downstream half of therotating entrance-pulley drum in a region where the moving belttangentially separates from this pulley drum.

[0005] In this space-limited “cusp region,” precise control of beltdistortion is desired because this is the place where very hot incomingmolten metal first contacts the moving belt.

[0006] A substitute for a rotating entrance-pulley drum was disclosed bySivilotti et al. in U.S. Pat. Nos. 4,061,178 and 4,061,177. Amultiplicity of hydraulic flotation “spools” defined and supported thebelt path. These spools were disclosed using absolute air pressure lessthan atmospheric—a partial vacuum—to exhaust coolant liquid away fromthe spools and to force the belt almost against the spools.

[0007] Forces associated with such partial vacuum have been found to beinsufficient to stabilize casting belts enough to ensure casting ofhigh-quality product. Sivilotti (in U.S. Pat. No. 4,061,177, column 19)disclosed coolant preheated to 40 to 70° C. to help stabilize the belts.

[0008] However, resulting high partial pressure of water vapor issuingfrom hot water limited the partial vacuum achievable by Sivilotti et al.

[0009] Moreover, water or coolant temperature even at 70° C. is too lowfor adequate belt preheat to enable casting high-quality product.

[0010] Yet, coolant temperature at 55 to 70° C. (131° to 158° F.)presents danger or scalding personnel if this hot coolant were to getout of control as through a defective belt or broken conduit.

[0011] Consequently, equipment disclosed in these patents did not solveproblems of suitably stabilizing a casting belt and ensuring casting ofhigh-quality product.

[0012] It is known that smooth solid objects can be “floated” very closeto smooth solid surfaces by means of fluid interposed between them underpressure. However, when one of the objects is flexible and is moving andalso is curved, serious problems arise, such as generation ofintolerable screeching noises and belt vibrations when attempting to usecompressed air for “floating” a casting belt moving along a curved,stationary support surface.

SUMMARY

[0013] I have found a non-rotating, fixed, rigid, convex, generallycylindrically curved, levitating “air pillow” belt-guiding apparatuswhich is much less complex than a multiplicity of spools with scaldinghot coolant and partial vacuum. Also, I find that this air-pillowapparatus can be devised to overcome or substantially reduce the aboveproblems. The air-pillow apparatus disclosed herein enables an endless,thin-gauge, flexible casting belt in a continuous casting machine to bedeflected, curved, or reversed in its course while making available thespace formerly occupied in most belt-type machines by the downstreamhalf of the rotating entrance-pulley drum. The space so saved becomesavailable for improved belt cooling and support apparatus to be employedin this critical zone which includes the above-defined “cusp region”where molten metal first contacts the casting belt.

[0014] In a preferred mode of the invention, levitating air (or othergas) is introduced under controlled pressure and volume into a thin,semi-sealed space or spaces between the moving curved inner surface of acasting belt and the convex-curved, generally cylindrical air-pillowapparatus, thereby enabling the casting belt to revolve in its usualpath, with only a minimum of friction. In addition, and advantageously,normal belt tension can be applied to the the belt during operation.

[0015] Preheating a casting belt controls thermally-induced strains inthe belt, thereby keeping the belt flat so that the solidifying moltenmetal being continually cast is protected from disturbance byunpredictable, sudden distortions which otherwise would occur due tothermally-induced strains in the belt where the belt is adjacent to hotmetal. Belt preheating enables casting high-quality product. Beltpreheating is disclosed in several U.S. Patents assigned to the Assigneeof this application.

[0016] Flowing room-temperature compressed air against a preheated beltdoes not much alter its preheat. On the other hand, contact of a hotbelt, for example with room-temperature coolant would considerablyreduce belt temperature where such coolant contacts the belt. Dry beltpreheating, for example by radiant heating, is facilitated by employingthe present invention. Among advantages of using dry preheating arethose resulting from avoiding use of dangerous, scalding-hot preheatingcoolant such as in the '178 and '177 patents discussed above. Also, ifwater is the coolant, steam is avoided. Moreover, using hot water in aroom where a casting machine is located will saturate ambient air withwater vapor. This air-borne moisture may condense as droplets on castingbelts and may cause minor explosions when such droplets are struck bymolten metal. Also, high humidity near a casting machine is debilitatingon workers performing jobs requiring alertness and continual carefulattention, with quick and skilled responses needed for controllingparameters of ongoing continuous casting.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Other objects, aspects, features and advantages of the presentinvention will become more fully understood from the following detaileddescription of presently preferred embodiments considered in conjunctionwith the accompanying drawings, which are presented as illustrative andare not necessarily drawn to scale or orientation and are not intendedto limit the invention. Large outlined arrows point “downstream” in alongitudinal (upstream-downstream) orientation, indicating the directionof product flow from entrance to exit of the continuous casting machine.

[0018]FIG. 1 is a side elevational view of a twin-belt continuousmetal-casting machine as seen from its “outboard” side, shown as anillustrative example of a continuous casting machine in which thepresent invention can be employed to advantage. Air-pillow apparatusembodying the invention is shown in the entrance region in an upper beltcarriage and also in a lower belt carriage.

[0019]FIG. 2 is a perspective elevational view of isolated-depressionair-pillow apparatus as seen looking downstream. The air-pillowapparatus is shown in the orientation it has in FIG. 1 wherein thisapparatus is mounted in an entrance region of an upper or lower beltcarriage.

[0020]FIG. 3 is a view similar to FIG. 2, but FIG. 3 showsisolated-depression air-pillow apparatus having perimetralair-throttling barriers.

[0021]FIG. 4 is an enlarged view of an end portion of theisolated-depression air-pillow apparatus as seen looking down fromposition 4—4 in FIG. 3.

[0022]FIG. 5 is an enlarged partial cross-sectional elevational view ofupper and lower isolated-depression air-pillow apparatus with theirrespective moving casting belts in the entrance region of a continuoustwin-belt casting machine, such as shown in FIG. 1. The section locationof FIG. 5 is indicated at 5—5 in FIG. 4.

[0023]FIG. 6 is a greatly enlarged partial perspective and sectionalview of a portion of isolated-depression air-pillow apparatus as seengenerally from position 6—6 in FIG. 4, looking diagonally upstream froman elevated viewing position. Two embodiments are shown of finepressure-extension grooves in an outward face of a perimetral seal.

[0024]FIG. 7 is similar to FIG. 6, but FIG. 7 shows a portion ofisolated-plateau air-pillow apparatus.

[0025]FIG. 8 is similar to FIG. 5, but FIG. 8 shows upper and lowerisolated-plateau air-pillow apparatus with their respective movingbelts.

[0026]FIG. 9 is a further enlargement of the entrance region shown inFIG. 5. FIG. 9 shows decreasing curvature (enlarging radii) oftransitional curves provided by the belt-path-determining shape of theair-pillow apparatus guiding moving belts into the moving mold.

[0027]FIG. 10 is an enlarged partial cross-sectional view showing acurved deflector which redirects an initial high-velocity flow of liquidcoolant for applying it flowing downstream along the lower belt.

[0028]FIG. 11 is a view of nested backup rollers as seen from position11—11 in FIGS. 10 and 12. These nested backup rollers have magnetizedfins with alternate N, S, N, S polarities, as disclosed and claimed inU.S. Pat. No. 5,728,036 referenced above.

[0029]FIG. 12 is a view similar to FIG. 10, wherein a modifiedembodiment of the apparatus of FIG. 5 includes multiple nozzles (onlyone nozzle is seen) for applying an initial high-velocity downstreamflow of liquid coolant onto the lower belt.

[0030]FIG. 13 is a view similar to FIG. 3, except that this modificationhas the isolated depressions configured as elongated semi-circulardepressions extending parallel to the direction of belt travel.

[0031]FIG. 14 is a view similar to FIG. 13, except that in thismodification one air-jet feeds into one unified levitating area for theentire air pillow apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] This specification will proceed in reference to twin-belt castingmachines, which typically have upper and lower carriages for revolvingupper and lower casting belts. The revolving belts define a moving moldcasting cavity or mold space between them. The belts are travelling fromthe entrance into the moving mold space and along the mold space to theexit. The belts bear and confine between them incoming hot molten metaland they cool and confine the resulting freezing molten metal forproviding a solidified metal product fed out from the exit.

[0033] In a twin-belt casting machine, the pass line, which is the pathfollowed by the freezing metal filling the mold M, is generallystraight. In a single-belt machine (not described herein), the pass linemay be a slightly curved convex path as seen from the side.

[0034] As used herein the terms “cylindrical surface,” “cylindricalshape,” “cylindrically shaped,” “cylindrical” and “cylinder” areintended to be broadly construed so as to include cylindrical surfaceshaving a circular curvature and cylindrical surfaces having a convexcurvature which varies from circular.

[0035]FIG. 1 shows a twin-belt casting machine 20 as seen from itsoutboard side. The lower and upper carriages are indicated at L and U.Through molten-metal-feeding equipment (not shown) known in the art,molten metal is introduced into the entrance end 22 of the moving moldcavity or mold space M (FIGS. 1, 5, 8, 9). This introduction of moltenmetal is schematically indicated by a large open arrow 24 shown at theleft. A continuously cast product P shown at the right in FIG. 1 emerges(arrow 26) from the exit end of moving mold cavity M.

[0036] The lower arid upper sides of the moving mold cavity M arebounded by revolving upper and lower endless, flexible, thin-gauge,metallic, heat-conducting casting belts 28 and 30, respectively. Thesebelts are cooled on their inner surfaces by fast-flowing liquid coolant,normally water. The two lateral sides of the moving mold space M arebounded by two revolving edge dams 32 as known in the art. In FIG. 1 anedge dam is shown guided into the entrance 22 by a crescentconfiguration of rollers 33. Upper belt 28 is driven (as shown by arrow36) by a rotatably-driven upper exit pulley drum 34 positioned above theexit (downstream) end of the moving mold cavity. Lower belt 30 and edgedams 32 are driven (as shown by arrow 37) by a rotatably-driven lowerexit pulley drum 38 positioned below the exit end of moving mold spaceM. Further information regarding such twin-belt casting machines is setforth in the above-referenced patents of Hazelett et al.

[0037] At the entrance end of the casting machine, the upper and lowercasting belts 28, 30 revolve respectively around non-rotating, fixed,rigid, convex-curved, cylindrical upper belt-levitating air-pillowapparatus 40 and similar lower air-pillow apparatus 42. Each air-pillowapparatus 40 and 42 includes an air-pillow shell 44, which is ageometric sector of a shell of cylindrical shape. Each shell 44 isperforated with at least one, and in most embodiments of the inventionwith a multiplicity of, air-jet bore passages 87 in nozzle bodies 85(FIGS. 5, 8, 9, 10 and 12). The included angle “A” (FIG. 1) spanned(subtended by) by the geometric shell sector 44 is the angle A ofguidance of a casting belt. Angle A may be in a range from a few degreesup to about 270 degrees. This shell sector A is shown in FIG. 1 as beingabout 180 degrees.

[0038] Except for corrosion-resistant materials used for coolanttransport, air-pillow shells 44 and their stiftening back members 46(FIGS. 1, 5 and 8) and end walls 48 (FIGS. 2, 3) as shown are made ofmachinery-steel plate and assembled by welding.

[0039] The volume enclosed by sector shell 44, stiffening back wallmember 46 and end walls 48 comprises a plenum chamber 52 which is used,as will be explained, for distribution 53 of air (gas) as shown in FIGS.1, 5, 8, 9, 10 and 12. Manual access to this plenum chamber is affordedthrough access ports in each end wall, which normally are closed bycovers 55 (FIGS. 1, 2, 3, 13 and 14). Mounting lugs 50 projecting fromopposite ends of the plenum chamber 52 are secured to a strut 57 whichstiffens the end wall 48. The term “air” as used herein applies to agaseous levitating agent and is intended to include ordinary air andfractions of ordinary air such as nitrogen, argon, carbon dioxide, orhelium, or any other gas or gaseous mixture that is suitable to use as alevitating agent.

[0040] In the embodiments of the invention as shown, compressed air 53,53′ is employed as the levitating agent for upper and lower castingbelts 28, 30. This levitating agent engages the respective belt as thebelt travels along a curved path in wrapped “floating” relationship pastthe upper or lower air-pillow apparatus 40 or 42. The moving belt isguided in “floating” relationship, being supported by (levitated by)compressed air. Compressed air 53 is fed into the plenum chamber 52through a suitable pipe or hose connection 51 (FIG. 1). This compressedair passes from the plenum chamber as shown by arrows 53 in FIGS. 5, 8,9, 10 and 12 into a multiplicity of vestibular passages 88 drilled inshell 44. These passages 88 lead into nozzle bodies 85 having fixedlythrottling air-jet bore holes 87 which issue levitating air 53′ intocontrolled levitating relationship with the travelling casting belt 28or 30. The length of air-jet bore holes 87 in a recent embodiment of theinvention is about 19 millimeters. The selection of a suitable diameterof nozzle bores 87 depends on the various embodiments described later,and is in a range from about 0.4 millimeter to 15 millimeters. Thediameter of jet-nozzle bore holes 87 in the embodiment shown in FIG. 5is 1.15 millimeters.

[0041] All reference to air pressure henceforth is to “gauge pressure,”i.e., pressure in relation to atmospheric pressure taken as zero. Thepressure of compressed air 53 supplied into plenum chamber 52 via airinlet 51 (FIG. 1) is about 850 kilopascals or about 8.5 bars, whichapproximates about 120 to 130 pounds per square inch (psi), commonlyavailable in industrial plants. After air flow 53 has passed throughvestibules 88 and through the throttling air-jet bore holes 87, theresultant belt-levitating air 53′ in a belt-levitating region locatedbetween air-pillow shell 44 and the concave, cylindrically curved innersurface of the traveling levitated casting belt 28 or 32 has an averagepressure, for example, of about 425 kilopascals or about 4.25 bars(about 60 to 65 psi), as will be explained presently. As shown in FIGS.2 through 6, 9 and 12, air-jet bore holes 87 feed levitating air 53′into the center of each shallow depression 80. As shown in FIGS. 7, 8and 10, the air-jet bore holes 87 feed levitating air 53′ spreading outfrom the center of each elevated plateau 100. A thickness of the endlesscasting belts 28 and 32 as shown herein is about 1.2 millimeters (about0.046 to about 0.048 of an inch).

[0042] Air-pillow shells 44, as shown in FIG. 1 have a radius R₁ (FIGS.5, 8 and 9) of about 305 millimeters (mm), (about 12 inches), and eachshell 44 spans (subtends) an included angle A (FIG. 1) of about 180°.Using air pillow apparatus of 610 millimeters diameter in a machine forexample such as shown in FIG. 1, the force exerted against each of tworeaches of each casting belt by the levitating air 53′ of the air pillowapparatus 40 or 42 in a direction parallel to the mold M, i.e. parallelto freezing product P, is about 125 newtons per millimeter of beltwidth. This force results in a tensile stress of about 10,000 newtonsper square centimeter of cross section in the casting belt 28 or 30.This tensile stress approximates the operating practice of the priorart.

[0043] The force exerted by pressure of levitating air 53′ where itcontacts the curved inner surfaces of casting belts 28, 30 normally isadjusted to provide a total upstream-directed force component that isslightly less than, or equal to, the effective total tensile forcesexerted in a downstream direction by the belt 28 or 30 acting upon itsrespective air pillow apparatus 40 or 42. This is to say, this totalupstream-directed force component is preferably between about 99 and 100percent of the effective total belt tensile forces or, at a minimum, 90percent. As a result, the casting belt 28, 30 may slide against the airpillow shells 44 though lightly. The contact of the travelling castingbelt against the convex peripheral belt-guiding surfaces of an airpillow shell is nearly or entirely eliminated. By maintaining someslight sliding contact as at semi-seals, such as perimetral seals 90 and90′ in FIGS. 4, 5 and 8 or at a seal 82 in FIG. 9, any significantunstable movements of the casting belt in any direction can beprevented. It is to be understood that, during continuous castingoperation, the pressure of levitating air 53′ may be adjusted slightlyupwardly so as to minimize wearing of the working surface against theinner surface of the moving belt and may be adjusted slightly downwardso as to diminish any incipient unstable movements of vibrations ornoises. The terms “levitate” or “levitating” or “levitated” hereininclude this situation wherein friction is relieved but some lightcontact and slight friction remain.

[0044] I have found that the air-pillow apparatuses described permitquiet operation of travelling curved flexible casting belts operatingunder tensile stress approximating customary practices of the prior art.

[0045] Isolated Depression Embodiments:

[0046] The invention is embodied basically in two complementary modes.Embodiments of the first mode employ an array of a multiplicity ofbroad, isolated, semi-sealed, shallow depressions 80 formed on theconvex exterior surface of cylindrically shaped air pillow shell 44(FIGS. 2 to 6, 9). These shallow depressions 80 constitute a majorportion of the total belt-levitating area of air-pillow shell 44.Shallow depressions as shown have a rectangular configuration which isalmost square. These shallow depressions 80 are shown bounded anddefined by a semi-sealing grid, i.e. an air-throttling barrier grid 82as shown in FIGS. 2 to 6 and 9. If this cylindrically shaped grid werelaid flat, it would be a rectangular grid. The outward surface of grid82 provides belt-supporting, belt-path-guiding, convex peripheralworking surfaces (faces) 82′ of the cylindrically shaped air-pillowshell 44. The grid 82 as shown may be described generally as definingand constituting an array of air-throttling surfaces (faces) 82′circumscribing a plurality of rectangular levitating shallowdepressions.

[0047] When enwrapped by a casting belt as shown in FIGS. 1, 5 and 9,the grid 82 and the concave, cylindrically-curved inner belt surfacedefine shallow cavities 80 depressed below the peripheral workingsurfaces 82′ of semi-cylindrical air-pillow shell 44. The grid 82′ andits convex working peripheral surfaces 82′ can be made integral withair-pillow shell 44 (FIGS. 2, 3, and 4).

[0048] In a preferred construction, however, the grid 82 is formed offlexible material, for example such as slippery plastic material whichis removably attached to air-pillow shell 44. This grid 82 is formedeither as a monolithic net of elongate elements, this net being cut orstamped from a sheet of suitable slippery plastic material or,alternatively, the grid 82 is formed by assembling a multiplicity ofseparate, elongated strips of suitable plastic material. Whether thegrid 82 is monolithic or is assembled from multiple strips, the flexiblematerial of which it is formed preferably is durably wear-resistant whensubjected to continual sliding contact of a moving casting belt 28 or30. The currently preferred slippery plastic material for constitutinggrid 82 is PTFE (polytetrafluoroethylene), marketed by DuPont undertheir trademark “Teflon.”

[0049] The monolithic grid or individual strips 82 preferably fit (nest)into closely conforming grooves 83 machined in the outer surface of eachair-pillow shell 44. Capture of the grid 82 nested in grooves 83 iscompleted by screws 89 (FIGS. 5, 6 and 9) and by the enwrappingrelationship of a casting belt as shown in FIGS. 1, 5 and 9. The depthof grooves 83 is such that peripheral working surfaces 82′ of amonolithic grid 82 (or equivalent assemblage of individual strips) areelevated above the floor of each thus-formed isolated, levitatingsemi-sealed shallow depression 80 by a small radial elevation “h” (FIG.6) in a range between about 25 microns and 2.5 millimeters. This radialprotrusion dimension “h” establishes the resulting assembled depth ofeach shallow depression 80.

[0050] When the shell 44 is machined as an integral construction ofshell 44 together with its semi-seals provided by air-throttling grid82, then dimension h is the height from the floor of each shallowmachined depression 80 to the belt-guiding, peripheral working surfaces82′ of this integral grid. FIG. 2 is intended to illustrate an integralconstruction of grid 82 aid shell 44, and also to illustrate a grid 82formed by a net (or by individual strips) assembled in nestedrelationship in grooves (not seen in FIG. 2) in the shell 44.

[0051] The working surfaces 82′ of grid 82 acting in conjunction withthe inner surface of a travelling casting belt provide a network ofair-throttling paths (semi-sealing paths) for the escape of pressurizedbelt-levitating air 53′ from each shallow depression 80. This escape orbelt-levitating air 53′ from the shallow levitating depressions 80advantageously serves for isolating pressure in each depression frompressures in neighboring depressions, because escaping air flows towardregions of lower pressure and avoids regions of higher pressure.Consequently, each levitating depression 80 acts as an isolated,belt-levitating area operating somewhat independently of the otherisolated depressions 80, thereby avoiding positive feedback effectsbetween air pressures in neighboring belt-levitating areas, and therebyavoiding generation of screeching noises and belt vibrations.

[0052] The combined totality of a resulting multiplicity of individual,somewhat independent, somewhat isolated, belt-levitating forces (appliedto the inner surface of an overlying moving belt wrapped around anair-pillow shell 44) created by pressure of levitating air 53′ in themultiplicity of shallow depressions 80 provides a substantially uniformupstream-directed levitating-air force on a moving belt, which (as isexplained above) is at least about 90 percent of the total effectivetensile forces in the associated revolving belt, with minor remainingupstream force, if any, on a moving belt being provided by some slightmechanical contact between a moving belt and portions of air-pillowapparatus.

[0053] An individual air-jet bore 87 is shown communicating with thecenter of the floor of each shallow depression 80 for feedingbelt-levitating air 53′ into the depression. As explained above, eachshallow depression is semi-sealed by the inner surface of the beltenwrapped around the air-pillow shell 44 and whose inner surface is veryclosely adjacent to or is lightly sliding against working surfaces 82′.Pressurized belt-levitating air is continually escaping, i.e.,exhausting, into the atmosphere by flowing over and along the workingsurfaces 82′ of grid 82 (FIGS. 5, 6, 9 and 12).

[0054] Isolated Plateau Embodiments:

[0055] Second-mode embodiments of the invention have an array of broad,isolated, air-throttling, levitating “plateaus” 100 (FIGS. 7 and 8, also10) positioned on the exterior of air-pillow shell 44. Isolated plateaus100 are defined and bounded by grooves (channels) 102 which provideair-escape (air-exhaust) pathways. In an overall, generalized view, thesecond-mode embodiments have reverse radial relationships as comparedwith the radial relationships of the first-mode embodiments as seen bycomparing FIGS. 7, 8 and 10 with FIGS. 5, 6, 9 and 12.

[0056] Isolated rectangular plateaus 100 have convex peripheral surfaces(faces) 100′. These surfaces 100′ are belt-supporting, guiding, convexperipheral working faces of the cylindrically shaped air-pillow shell 44(FIGS. 7, 8 and 10).

[0057] The plateaus 100 and their working surfaces 100′ can be madeintegral with air-pillow shell 44 as shown in FIG. 7, except that in anintegral construction there are no screws 109. in a preferredconstruction, however, the individual plateaus 100 are formed offlexible material, for example such as plastic material that is durablywear-resistant when subjected to continual contact of a moving castingbelt 28 or 30, for example such as the currently preferred slipperyplastic material described above. These individual rectangular plateaus100 preferably fit (nest) into closely conforming rectangulardepressions 101 (FIGS. 8 and 10) formed in the outer surface of eachair-pillow shell 44. Capture of individual plateaus 100 nested in theirdepressions 101 is completed by screws 109 (FIG. 7) and by theenwrapping relationship of a casting belt as shown in FIGS. 1, 8 and 10.

[0058] Levitating air 53′ is shown issuing from the center of eachworking surface 100′, being fed by means of a nozzle body 85 (FIGS. 8,10) having an air-jet bore hole 87. Plateau working surfaces 100′ areshown arranged in a rectangular array. These working surfaces serve boththe functions of providing belt-levitating areas for supportingbelt-levitating pressurized air 53′, and also they provide asemi-sealing function, acting in association with the inner surface ofan overlying belt, i.e., an air-flow throttling function. Each plateauedworking surface 100′ provides a semi-seal acting against the movinginner surface of the overlying casting belt 28 or 30. Thus, thelevitating air 53′ issues from each air-jet bore hole 87 and escapes asa very thin film flowing outwardly over each working surface 100′ fromthe centralized air jet. The outwardly-flowing belt-levitating air 53′endures speed-induced frictional pressure loss; i.e. it is throttled asit flows outwardly over each surface 100′, arid this escaping air slipsinto the system or network of air-exhaust grooves 102, whence theescaping air returns to the atmosphere when it reaches the edges of theair-pillow shells 44. Isolated-plateau embodiments of the invention workwell only when the belt is quite free from irregularities of surfaceshape or flatness.

[0059] Both the embodiments of the first mode of the invention, whichincludes isolated shallow depressions 80, and the embodiments of thesecond mode of the invention, which includes isolated plateaus 100, maybe characterized together as arrays of isolated belt-levitating areaswith intervening air-escape paths.

[0060] Embodiments Having Transition Curves:

[0061] In FIGS. 5 and 8, the radius R₁ is shown to be the radius ofperipheral working surfaces 82′ and 100′ of respective air-pillow shells44 having isolated depressions 80 and isolated plateaus 100. Thus, theseworking surfaces 82′ and 100′ conform with a circular cylindricalsurface, and so they simulate the upstream half of the exterior surfaceof a rotating pulley drum. Points 91 in FIGS. 5 and 8 at the entrance 22of the moving mold M are located at the downstream edges of perimetralseals 90′. These points 91 are tangent points whereat moving belts 28and 30 theoretically become bent (flexed) from circular cylindrical tostraight planar configuration travelling in spacedparallel-relationship, defining moving mold M between them.

[0062] Given the available constraints upon a casting belt of normalthickness and springiness, such an abrupt flexing of a belt from thecircular cylindrical configuration of the peripheral working surface ofan air-pillow shell 44 to a straight planar configuration does not infact occur. The undesirable result is an indeterminate path for thecasting belt and the consequent unsteady or lapsed contact of thefreezing product against the casting belt, thereby permittingundesirable surface liquation and alloy segregation.

[0063] When casting belts 28, 30 of normal and greater thickness areemployed, a locally variable radius R+ (FIG. 9) of the casting belt asdefined by its guides is advantageously progressively increased above R₁in a flexural transition region 114 where the moving casting beltapproaches and enters the mold space M. This region 114 of transitionalradius R+extends downstream from points 122 to mold entrance points 120.In this transitional region, the curvature 1/R+ (the reciprocal of thelocal radius) of each belt is advantageously progressively decreased ina tapering relationship decreasing all the way down to zero at atransitional tangent point 120 (FIG. 9) at the mold entrance, where thetwo belts become straight, travelling in spaced parallel planes. Theneed for this tapering-off (progressive decrease) of curvature arisesfrom the elastic stiffness or springiness of casting belts of suitablyhigh thickness, a stiffness which otherwise would distort the belt pathwhere the belt leaves the downstream end 91 (FIGS. 5 and 8) of an airpillow shell 44.

[0064] The tapering-off of curvature in FIG. 9 begins at points 122 inthis magnified cross-sectional view and continues to mold-entrancepoints 120. Downstream, past a centerline 45 (FIG. 9) of the major partof each air pillow apparatus, the belt 28 or 30 is guided into the moldspace M by stationary elements 116 as disclosed and claimed in PCTapplication WO 98/01247 of Kagan et al., which application is assignedto the same assignee as the present invention. There are multiple,spaced, parallel elements 116 magnetized by reach-out permanent magnetsproviding magnetic attraction acting in opposition to hydrodynamicbelt-levitating forces for providing belt guidance and stabilization.

[0065] The belt-path curvature 1/R+ gradually decreases from points 122to points 120, becoming zero at the casting belts' tangent points 120.Downstream from tangent point 120, the belts are constrained to bestraight, travelling in spaced parallel planes. (Note that themultiple-radii cross-sectional shape of an air pillow shell with aprogressively increasing radius R+ in transitional region 114 is still a“cylinder” and a “cylindrical surface”; see for instanceMerriam-Webster's Collegiate Dictionary, tenth edition [1993]).

[0066] An ideal, gradually straightening curved casting-belt path 114plotted in FIG. 9 between points 120 and points 122 3 follows theformula: y =ax as in a railway transitional curve, where “a” in afull-scale casting machine is on the order of 1/70,000. Both dimension xand dimension y are measured in millimeters. x is measured to the left,i.e., in an upstream direction from new tangent points 120. Thesuccessive number values for dimension y are shown for convenienceprinted within the passage space of a metal-feeding nozzle 62 supportedbetween clamps 64. These y dimensions apply separately to each of thetwo belts—upward for the upper belt 28 from the upper surface of nozzle62 (which aligns with the plane of the planar mold surface of upper belt28) and downward for the lower belt 30 from the lower surface of thisnozzle (which aligns with the plane of the planar mold surface of lowerbelt 30).

[0067] Magnetic attraction force from elements 116 is usefully appliedin guidance of a moving casting belt in the critical areas 114 ofreducing curvature, since the wrapping pressure on the levitating airpillow shell 44 provided by tension of the casting belt in this region114 of reduced curvature is naturally less than the wrapping pressureacting on the major portion 110 of the air pillow apparatus where theradius is a constant R₁.

[0068] Since the tapering-off of curvature of the casting belts isgradual along the transitional region 114, the elastic bending springforce likewise tapers off gradually. Thereby, advantageously, therespective casting-belt paths are under determinate control throughouttheir travel past the nozzle 62 and into the mold M; the springiness ofthe belt does not deflect either belt from its intended guidance path.

[0069] Instead of a railway transitional curve, such as y=ax³, asequence of smooth curves of decreasing curvature may be used in lesscritical applications.

[0070] FIGS. 3-5, 8, 13 and 14 show embodiments of the invention whereinthere is employed an elongate perimetral air-throttling seal 90, or 90′,which is a little higher above the convex peripheral working face thanthe other air-throttling or supporting surfaces. Such a perimetral sealholds a minimal air pressure (above atmospheric) over the entire convexface of the air-pillow shell 44. Throttled air finally escapes to theatmosphere past this semi-seal 90, 91′ at the perimeter of each airpillow shell in apparatus 40 or 42. The upper and lower horizontalcourses 90′ of these perimetral air-throttling seals 90 assist incontrolling the path of the casting belt 28 or 30 where they enter uponand leave the air-pillow shell 44, defining for such shells of circularcylindrical shape theoretical belt-flexure tangent points 91. A suitablematerial for semi-seals 90 is polyamide (nylon) in the form of bunchedand twisted strands, which is commercially available as strip-packingmaterial. Other suitable wear-resistant, relatively flexible slipperymaterial may be used.

[0071]FIG. 6 shows in perspective a pattern or “tread” of shallow finefriction-reducing grooves 94 and 95 of rectangular cross section cut orimpressed into the outward surface, the working surface of a modifiedperimetral seal 92. Such a modified seal 92 may be used in place orplain nylon air-throttling seal 90. Grooves 94 oriented parallel withbelt motion communicate with a deeper transverse groove 95 extendingadjacent to a perimetral air-throttling lip 97. Thsee grooves 94 and 95spread the pressure of the confined pressurized levitating air 53′ overmuch of the face of the seal 92, thereby reducing friction, between thisseal and the moving casting belt 28 or 30, and rendering contact withthe casting belt more uniform.

[0072] At the lower left of FIG. 6 is shown a perimetral air-throttlingseal 93 whose working surface has another pattern or “tread” offriction-reducing grooves 96 and 98. Instead of the rectangular-shapedgrooves 94 and 95 of seal 92, the grooves 96 and 98 have a shallowscalloped shape. Shallow transverse groove 98 extends adjacent to aperimetral lip 99.

[0073] The perimetral seal 90 is advantageously used in connection withthe first and second modes of embodiment of the invention, describedabove. The employment of the perimetral seal 90 also enables realizationof a third mode of embodiment of the invention, namely, the merging ofisolated depressions into, at the limit, a parallel array of shallowcircumferential channels 86 (FIG. 13) which are isolated from each otherby intervening parallel circumferential ridge strips 81 formed ofslippery belt-supporting material similar to that which forms grid 82.Working surfaces 81′ of these circumferentially oriented ridge strips 81do not provide significant air-throttling action. To protect the tensedcasting belt from significant local transverse sagging (scalloping) orbending, such strips 81 are continuous in a circumferential direction inthe array shown in FIG. 13 (wherein only portions of the perimetral seal90 are seen) Each circumferential channel 86 is individually fed withpressurized belt-levitating air 53′ by a centrally located nozzle body85 having an intermediate-sized diameter air jet 87′.

[0074] In FIG. 14 one large nozzle body 85 having a very large diameterair jet 87″, centrally located, covers with pressurized levitating air53′ the whole outer surface of a shell 44 within the perimetral seal 90.However, to use only one such central large air jet 87″, air-throttlingaction over the working surfaces 81′ of ridge strips 81 (FIG. 13) mustbe substantially prevented, lest lowered levitation occur toward theinboard and outboard ends of the air-pillow shell 44. To avoid suchthrottling by working surfaces 81′ (FIG. 13), the ridge strips areinterrupted with numerous transverse gaps 78 (FIG. 14) having acircumferential length of less than about 2 degrees (less than about 9to 10 millimeters), thereby providing numerous island ridge strips 79for transversely distributing levitating air 53′ without significantpressure drop to all circumferential channels 86 within the peripheralseal 90. Thereby is provided a single interconnected unifiedbelt-levitating area 93 encompassing the whole exterior surface of ashell 44 within its perimetral seal 90.

[0075] Whatever the configuration in FIG. 13 or 14, pulling or saggingof the tensed belt into the circumferential channels 86 must beminimized. To this end, these channels 86 are to be no wider than about150 times the thickness of the casting belt being used.

[0076] Magnetic Backup Rollers:

[0077] In FIGS. 10 and 12, moving belts are shown being guided,stabilized and backed up by backup rollers 130 having magnetized fins asdescribed and claimed in my U.S. Pat. No. 5,728,036, assigned to thesame assignee as the present invention. The rotatable shafts 132 andencircling fins 134 are formed of magnetically soft ferromagneticmaterial. Fins 134 are magnetically energized in alternate north andsouth polarities (N and S in FIG. 11) by permanent collar magnets 133.“Reach-out” magnetic material may be used advantageously in these collarmagnets. These backup rollers 130 may advantageously be assembled closertogether than usual by staggering relative positioning of fins 134 topermit interdigitating the fins of one roller to nest between the finsof an adjacent roller as in FIG. 11.

[0078] Especially when backup rollers 130 are used, instead of using anarray of magnetized hydrodynamic backup elements 116 (FIG. 9), it isessential to cool the casting belts 28, 30 immediately adjacent to moldentrance 22 by a fast-moving layer 163 of liquid coolant, normallywater. This fast-moving coolant layer 163 advantageously is applieddirectly to the belt from air pillow apparatus 40 or 42, because absenceof a rotating entrance-pulley drum eliminates limitations imposed by aprior-art “cusp region” as described in the Background.

[0079] In FIG. 10 this fast-moving coolant 163 is applied from atransverse deflector 150 having a working shape similar to thatdisclosed in U.S. Pat. No. 3,041,686 of Hazelett et al. This deflector150 with its curved area 160 may be made integral with the back wall 46of the air pillow apparatus as shown in FIG. 10. Pressurized coolant 147is supplied from a header 152 having a plurality of nozzles 154 (onlyone is seen), whence coolant impinges as jets 156 at a small angleagainst the deflector 150. There, the coolant spreads sideways to becomea moving film 158 which races around curve 160 to leave the deflector asa relatively flat, fast-moving sheet 162 which creates coolant layer163.

[0080] In FIG. 12 the application of fast-travelling coolant layer 163onto the casting belt is accomplished by a plurality of nozzles 146(only one is seen). These nozzles and their coolant-feed passages 144are shown constructed integral with the air pillow apparatus.Conveniently, a header 142 to enclose a coolant plenum 140 is fittedright into part of the volume of the air plenum chamber 52, as shown inFIG. 12, where only a portion of the header 142 is shown. Emergingcoolant jets 149 from nozzles 146 create fast-moving coolant layer 163.The direction of coolant flow is shown by arrows 147. Plugs 148 sealpassages 144 where required.

[0081] Magnetized hydromagnetic elements 116 shown in outline in FIG. 9as disclosed and claimed in PCT application of Kagan et al, referencedabove, may be employed rather than the backup rollers 130 in FIG. 12.Then, the coolant jets 149 sweep downstream and clear away from betweenspaced parallel elements 116 spent hydrodynamic coolant emerging fromthe outlets (not shown) in the elements 116. Further, these powerfulcoolant jets 149 serve to maintain a fast-moving flow of coolant layer163 continuing downstream just past downstream ends (not shown) ofelements 116.

[0082] Preheating the casting belts ahead of the entrance 22 to the moldM prevents unwanted belt distortion and hence permits production ofimproved product as explained in U.S. Pat. No. 3,937,270 of Hazelett etal., assigned to the same assignee as the present invention. The effectof preheating is thoroughly analyzed and illustrated in three U.S.patents of Hazelett and Wood, assigned to the same assignee as thepresent invention. U.S. Pat. No. 4,002,197 discloses liquid and steammeans of preheating but especially radiant preheating as by intensiveinfra-red heaters. U.S. Pat. No. 4,062,235 discloses devices for sensingthe warping or thermally induced movement of a casting belt in the mold,that is, sensing the beneficial effect of belt preheating. U.S. Pat. No.4,082,101 discloses devices to ensure that the coolant for the belts inthe mold covers barely more than the area of the belt touched by hotmetal in the mold. U.S. Pat. No. 5,133,402 of Ross discloses another drymethod of belt preheating, the method of electromagnetic inductivepreheating at a frequency, for instance, of 3,000 hertz applied througha loop of copper pipe near to the casting belt surface, through whichpipe flows water to keep the copper from melting because of the highamperage.

[0083] The compressed air which is employed to levitate a casting beltas it wraps upon the air pillow apparatus contains or absorbs only asmall amount of heat energy. The adjacent flow of compressed air doesnot much alter the preheat of a casting belt. Any contact of the beltwith water or liquid coolant would, on the contrary, dominate thetemperature of the belt, regardless of heat previously applied to it.While air pillow apparatus disclosed herein would make possible (as itwas not done by Sivilotti) the use of heated water for belt preheatingat temperatures as high as 93 degrees C. (200° F.), such heated coolantprocedure is complicated and is a radically inefficient use of energy.Moreover, radiant heat, or other dry, nonwetting heating applied to thebelt in proximity to the air pillow apparatus 40 and 42 is efficient andversatile in raising the temperature of an air-levitated casting belt toa desired preheat to a temperature between about 80° C. (about 176° F.)and about 150 degrees C. (about 302 degrees F.).

[0084] The use of a levitating fluid reduces or eliminates the contactpressure of the belts sliding against the supporting surfaces providedby the air pillow apparatus and hence reduces thermal conductionresulting from such contact. If the levitating fluid is air, even coolair, then the belts can still retain nearly all of their applied energyof preheat and not lose it to the guiding sliding surfaces. Without thispartial or full levitation by air, substantial preheat would be drawnaway from the casting belts as they slide over their supports. Moreover,any belt-preheat liquid applied anywhere near the mold entrance, near tomolten metal, would require careful disposal to avoid explosion.Compressed air at and below normal shop-air pressure as described isreadily available, is easily handled, and conveniently may be allowed toescape to ambient as described.

[0085] Although specific presently preferred embodiments of theinvention have been disclosed herein in detail, it is to be understoodthat these examples of the invention have been described for purposes ofillustration. This disclosure is not to be construed as limiting thescope of the invention, since the described methods and apparatus may bechanged in details by those skilled in the art of continuous casting ofmetals, in order to adapt these methods and apparatus to be useful inparticular casting machines or situations, without departing from thescope of the following claims. For instance, the foregoing discussionhas been in terms of a nearly horizontal twin-belt casting machinehaving upper and lower carriages, whereas the invention may be embodiedand employed in casting machines operating at any angle from horizontalto vertically downward. Again, the invention can be embodied andemployed in terms of single-belt casters having a relatively flatcasting zone. It is understood that downstream equipment might bearranged to permit the use of coolant layers 163 traveling across thecasting belts instead of longitudinally along them. Or perimetral sealsmight be multiple rather than unitary.

I claim:
 1. Air-pillow apparatus for guiding a moving, flexible, tensed,heat-conductive casting belt along a cylindrically shaped path whereinthe cylindrically shaped path is suitable for guiding such a castingbelt moving toward an entrance into a mold space of a continuous castingmachine, said air-pillow apparatus comprising: a plurality of stationarybelt-guiding elements defining the cylindrically shaped path; and saidbelt-guiding elements being arranged for association with pressurizedair for applying pressurized air in belt-levitating relationship againsta cylindrically curved inner surface of such a casting belt moving alongthe cylindrically shaped path.
 2. Air-pillow apparatus claimed in claim1, further comprising: a fixed, stationary support for said belt-guidingelements having said belt-guiding elements thereon; said support havingat least one passage for feeding pressurized air into contact with saidbelt-guiding elements; and said support having mounting members formounting the air-pillow apparatus in fixed, stationary position in acontinuous casting machine near the entrance into the mold space. 3.Air-pillow apparatus claimed in claim 2, wherein: said at least onepassage includes a nozzle for controlling pressure of pressurized airbeing fed into contact with said belt-guiding elements.
 4. Air-pillowapparatus claimed in claim 2, wherein: said belt-guiding elements havestationary surfaces for facing outward toward a cylindrically curvedmoving inner surface of such a casting belt moving along thecylindrically shaped path; and said surfaces of said belt-guidingelements include suitable, durable, wear-resistant, slippery material.5. Air-pillow apparatus claimed in claim 1, further comprising: anelongated, stationary air-throttling barrier extending across thecylindrically shaped path for positioning generally transverse to motionof such a casting belt moving along the cylindrically shaped path. 6.Air-pillow apparatus claimed in claim 5, further comprising: saidelongated air-throttling barrier having a stationary surface facingoutward for facing toward a cylindrically curved moving inner surface ofsuch a casting belt moving along the cylindrically shaped path; and saidsurface of said elongated air-throttling barrier havingpressure-extension grooves therein.
 7. Air-pillow apparatus claimed inclaim 6, further comprising: a stationary perimetral seal extendingaround said cylindrically shaped path for positioning in operativeassociation with a cylindrically curved moving inner surface of such acasting belt moving along the cylindrically shaped path for restrictingescape of pressurized air away from the curved moving inner surface ofsuch a casting belt; and said elongated air-throttling barrier is aportion of said perimetral seal.
 8. Air-pillow apparatus claimed inclaim 7, further comprising: a lip on said elongated air-throttlingbarrier; said lip extending longitudinally along said elongatedair-throttling barrier; said pressure-extension grooves in said surfaceof said elongated air-throttling barrier including an elongated groovein said surface extending longitudinally along said elongatedair-throttling barrier; said elongated groove being adjacent to saidlip; said pressure-extension grooves including a plurality of spacedparallel grooves communicating with said elongated groove and being onan opposite side of said groove from said lip; and said spaced parallelgrooves being oriented generally perpendicular to said elongated groovefor said spaced parallel grooves to be positionable generally parallelwith the motion of such a casting belt moving along the cylindricallyshaped path and for said spaced parallel grooves to be positionable incommunication with pressurized air in belt-levitating relationshipagainst a cylindrically curved moving inner surface of such a castingbelt moving along the cylindrically shaped path.
 9. Air-pillow apparatusclaimed in claim 8, wherein: said elongated groove is deeper than saidspaced parallel grooves communicating with said elongated grooves. 10.Air-pillow apparatus claimed in claim 2, further comprising: said fixed,stationary support having said belt-guiding elements thereon being amember having a convex outer surface; said belt-guiding elements beingon said convex outer surface; and said convex outer surface conforminggenerally with and being spaced inwardly from the cylindrically shapedpath defined by said outwardly facing, stationary surfaces of saidbelt-guiding elements.
 11. Air-pillow apparatus claimed in claim 1,wherein: the cylindrically shaped path has a constant radius R1. 12.Air-pillow apparatus claimed in claim 11, wherein: said convex outersurface spans an angle “A” of about 180°; and the constant radius R1 hasa length of about 305 millimeters (about 12 inches).
 13. Air-pillowapparatus claimed in claim 11, wherein: the cylindrically shaped pathincludes a cylindrically shaped flexural transition region of variableradius R+; the variable radius R+ of said cylindrically shaped flexuraltransition region progressively increasing in length relative to saidlength of constant radius R1 for progressively decreasing curvature ofsaid cylindrically shaped flexural transition region for reducingflexure of such a casting belt moving along the cylindrically shapedtransition region toward an entrance into a mold space of a continuouscasting machine.
 14. Air-pillow apparatus claimed in claim 13, wherein:said cylindrically shaped flexural transition region of variable radiusR+ extends along a gradually straightening curve.
 15. Air-pillowapparatus claimed in claim 14, wherein: said gradually straighteningcurve is similar to a railway transitional curve.
 16. Air-pillowapparatus claimed in claim 14, wherein: said air-pillow apparatus isadapted for guiding such a casting belt moving toward an entrance into amold space in a continuous casting machine wherein the mold spaceextends substantially flat from the entrance along a generally straightdownstream direction in the continuous casting machine; said graduallystraightening curve follows a formula: Y=aX³; where “a” is on the orderof 1/70,000 and both dimension X and dimension Y are measured inmillimeters; dimension X is measured in a direction away from theentrance; and said direction away from the entrance is opposite to saiddownstream direction.
 17. Air-pillow apparatus claimed in claim 14,wherein: said air-pillow apparatus is adapted to be installed in acontinuous casting machine near an entrance into a mold space in themachine wherein said mold space extends substantially flat from theentrance along a generally straight downstream direction and wherein themachine has a plurality of members positioned near the entrance into themold space for guiding such a casting belt moving along a portion ofsaid cylindrically shaped flexural transition region and into saidentrance; said portion of said cylindrically shaped flexural transitionregion extends along said gradually straightening curve; and saidgradually straightening curve has a curvature which becomessubstantially zero at the entrance into the mold space, therebyproviding gradually decreasing stress within such a casting belt movingalong said portion of said cylindrically shaped flexural transitionregion of gradually decreasing curvature and into said entrance, saidgradually straightening curve initially having curvature with the radiusR₁ followed by an increasing variable radius R+whose reciprocal 1/R+becomes substantially zero at said entrance for providing substantiallyzero curvature at the entrance, whereby such a moving casting belttravels through the entrance without significant flexure at the entranceand continues travelling downstream from the entrance along saidgenerally straight downstream direction.
 18. Air-pillow apparatusclaimed in claim 10, further comprising: said member being a cylindricalshell; end walls and a back member secured to said cylindrical shellenclosing a plenum chamber adjacent to an inner concave surface of saidcylindrical shell; said belt-guiding elements forming a stationary gridon said convex outer surface; said grid having a generally rectangularpattern with belt-guiding elements of the rectangular pattern formingwalls of a multiplicity of rectangular depressions on said convex outersurface; said convex outer surface forming floors of said rectangulardepressions; and said cylindrical shell having a multiplicity ofpassages extending therethrough from said concave inner surface to saidconvex outer surface for providing communication from the plenum chamberthrough floors of the rectangular depressions for feeding pressurizedair from the plenum chamber into said shallow depressions. 19.Air-pillow apparatus claimed in claim 18, wherein: individual passagesprovide communication from said plenum chamber through respective floorof individual rectangular depressions for individually feedingpressurized air into respective depressions.
 20. Air-pillow apparatusclaimed in claim 19, further comprising: a plurality of air-pressurecontrolling nozzles; and nozzles of said plurality being mountedindividually in respective passages.
 21. Air-pillow apparatus claimed inclaim 18, further comprising: a monolithic grid having belt-guidingelements of suitable, durable, wear-resistant, slippery materialarranged in said generally rectangular pattern; said convex outersurface of said cylindrical shell having a grid of grooves matching saidgenerally rectangular pattern of said monolithic grid; said monolithicgrid being mounted in said grid of grooves in snugly fittingrelationship therein; said monolithic grid protruding by a smallelevation “h” above the floors of said rectangular depressions; and saidsmall elevation “h” being in a range between about 25 microns and about2.5 millimeters.
 22. Air-pillow apparatus claimed in claim 18, furthercomprising: a multiplicity of strips of suitable, durable,wear-resistant slippery material; said convex outer surface of saidcylindrical shell having a grid of grooves matching said generallyrectangular pattern; said strips being mounted in said grooves in snuglyfitting relationship therein for forming said grid having a generallyrectangular pattern; said strips protruding by a small elevation “h”above the floors of said rectangular depressions; and said smallelevation “h” being in a range between about 25 microns and about 2.5millimeters.
 23. Air-pillow apparatus claimed in claim 10, furthercomprising: said member being a cylindrical shell; end walls and a backwall secured to said cylindrical shell enclosing a plenum chamberadjacent to an inner concave surface of said cylindrical shell; and saidbelt-guiding elements being arranged in a predetermined pattern on saidconvex outer surface of said cylindrical shell.
 24. Air-pillow apparatusclaimed in claim 23, wherein: said belt-guiding elements are elongated;said elongated belt-guiding elements are in spaced parallelrelationship; said spaced parallel elongated belt-guiding elementsextend along said cylindrically shaped path in a circumferentialdirection generally parallel with movement of such a casting belt movingalong the cylindrically curved path; and spaces between said spacedparallel elongated belt-guiding strips define channels having a widthnot exceeding about 150 times a thickness of such a casting belt movingalong the cylindrically shaped path; such thickness is in a range fromabout 0.3 mm (about 0.012 of an inch) to about 2 mm (about 0.079 of aninch); and said cylindrical shell has passages extending therethroughproviding communication between the plenum chamber and said channels.25. Air-pillow apparatus claimed in claim 23, wherein: said belt-guidingelements are rectangular plateaus arranged in a rectangular grid patterndefining channels therebetween whose floors are said convex exteriorsurface; and said cylindrical shell has passages extending therethroughand extending out through central points on outer surfaces of saidrectangular plateaus.
 26. Air-pillow apparatus claimed in claim 25,wherein: said plateaus protrude above said floors by an elevation “h”;and said elevation “h” is in a range between about 25 microns and about2.5 millimeters.
 27. Air-pillow apparatus for guiding a moving,flexible, tensed, heat-conductive casting belt along a cylindricallyshaped path wherein the cylindrically shaped path is suitable forguiding such a casting belt moving toward an entrance into a mold spaceof a continuous casting machine, said air-pillow apparatus comprising: amultiplicity of spaced, stationary elements having spaces therebetween;said spaced, stationary elements having stationary belt-guidingsurfaces; said belt-guiding surfaces being arranged along a convex,cylindrically shaped path; said belt-guiding surfaces facing outwardlyalong said convex, cylindrically shaped path for guiding such a castingbelt moving along said path with a cylindrically curved moving innersurface of the moving belt facing said belt-guiding surfaces; and saidair-pillow apparatus having at least one passage for feeding pressurizedair into said spaces between said elements for providing pressurized airin levitating contact with said cylindrically curved moving innersurface of the moving belt.
 28. Air-pillow apparatus claimed in claim27, wherein: said tensed belt exerts a first force component ofpredetermined magnitude directed toward said air-pillow apparatus; saidpressurized air feeding into said spaces between said elements iscontrollable for providing controlled pressurized air in levitatingcontact with said cylindrically curved moving inner surface of themoving belt for exerting on said cylindrically curved moving innersurface a second force component having a magnitude which is at leastabout 90% of said predetermined magnitude of said first force component;and said second force component is directed away from said air-pillowapparatus and is in opposition to said first force component. 29Air-pillow apparatus claimed in claim 28, wherein: said pressurized airfeeding into said spaces between said elements is controllable forproviding controlled pressurized air in levitating contact with saidcylindrically curved moving inner surface of the moving belt forexerting on said cylindrically curved moving inner surface a secondforce component having a magnitude which is in a range between about 99%and 100% of said predetermined magnitude of said first force component;and said second force component is directed away from said air-pillowapparatus and is in opposition to said first force component. 30.Air-pillow apparatus claimed in claim 29, further comprising: said moldspace extending substantially flat from the entrance along a generallystraight downstream direction; said mold space having an upstreamdirection opposite to said downstream direction; said convex,cylindrically shaped path spanning an included angle of about 180°; saidconvex, cylindrically shaped path having a radius R1 having a length ofabout 305 millimeters (about 12 inches); and said controlled pressurizedair in levitating contact with said cylindrically curved moving innersurface of the moving belt exerting a force component in the upstreamdirection which is about 250 newtons per millimeter of belt width. 31.Air-pillow apparatus claimed in claim 27, further comprising: a supporthaving an exterior of generally convex, cylindrical shape; and saidspaced, stationary elements being on said exterior of said support. 32.Air-pillow apparatus claimed in claim 31, further comprising: saidspaced stationary elements being a grid on said exterior of saidsupport; said grid extending along said convex, cylindrically shapedpath; and said belt-guiding surfaces being outwardly facing surfaces ofsaid grid.
 33. Air-pillow apparatus claimed in claim 32, furthercomprising: said belt-guiding surfaces of said grid being in a generallyrectangular pattern.
 34. Air-pillow apparatus claimed in claim 33,further comprising: said grid on said exterior of said support defininga multiplicity of depressions on said exterior of said support; saiddepressions facing outwardly toward the cylindrically curved movinginner surface of the moving belt; and said air-pillow apparatus having amultiplicity of passages communicating with said depressions for feedingpressurized air into said depressions for being in levitating contactwith said cylindrically curved moving inner surface of the moving beltas the belt moves over said depressions.
 35. Air-pillow apparatusclaimed in claim 34, further comprising: a plurality of air-pressurecontrolling nozzles; said passages communicating individually with saiddepressions; and one of said nozzles being in each of said passage forcontrolling pressure of pressurized air feeding into the depressions forcontrolling pressure of air in levitating contact with saidcylindrically curved moving inner surface of the moving belt as the beltmoves over said depressions.
 36. Air-pillow apparatus claimed in claim35, further comprising: said support being a cylindrically shaped shellhaving said exterior of generally convex, cylindrical shape; saidcylindrically shaped shell having an interior communicating with aplenum chamber; and said multiplicity of passages extending from saidplenum chamber through said shell into said depressions.
 37. Air-pillowapparatus claimed in claim 23, wherein: said belt-guiding elementscomprise a plurality of ridge strips extending along said cylindricallyshaped path in a circumferential direction; said ridge strips definingcircumferential channels therebetween; said ridge strips beinginterrupted by transverse gaps; said transverse gaps havingcircumferential lengths of less than about 10 millimeters (about 0.39 ofan inch); and said cylindrical shell having at least one passagetherethrough providing communication from said plenum chamber into acircumferential channel; and said at least one passage being positionedin a centralized location among said ridge strips.
 38. Air-pillowapparatus claimed in claim 37, further comprising: a nozzle forcontrolling pressure of pressurized air; and said nozzle beingassociated with said at least one passage for controlling pressure ofair flowing from said plenum chamber through said passage. 39.Air-pillow apparatus claimed in claim 23, wherein: said air-pillowapparatus is adapted for guiding such a casting belt moving toward anentrance into a mold space in a continuous casting machine wherein themold space extends from the entrance along a downstream direction; saidair-pillow apparatus further comprising: a coolant deflector associatedwith said back wall; said coolant deflector having a curved area forapplying coolant to an inner surface of such a casting belt moving inthe downstream direction near said entrance; and said curved area isconfigured for applying coolant in the downstream direction to saidinner surface.
 40. Air-pillow apparatus claimed in claim 39, wherein:said deflector is formed integral with said back wall.
 41. Air-pillowapparatus claimed in claim 23, wherein: said air-pillow apparatus isadapted for guiding such a casting belt moving toward an entrance into amold space in a continuous casting machine wherein the mold spaceextends from the entrance along a downstream direction; said air-pillowapparatus further comprising: a plurality of coolant applicationnozzles; and said coolant application nozzles being aimed generally inthe downstream direction for applying coolant to an inner surface ofsuch a casting belt moving in the downstream direction near saidentrance.
 42. Air-pillow apparatus claimed in claim 41, furthercomprising: a coolant plenum within said plenum chamber; and saidcoolant plenum communicating with said coolant application nozzles forfeeding coolant into said nozzles.
 43. Air-pillow apparatus claimed inclaim 42, wherein: said coolant nozzles are formed integral with theair-pillow apparatus.
 44. Air-pillow apparatus claimed in claim 2,wherein: said cylindrically shaped path is suitable for dry preheatingof such a casting belt moving toward an entrance into a mold space of acontinuous casting machine.
 45. Air-pillow apparatus for use in acontinuous casting machine having at least one endless, flexible,tensed, heat-conductive casting belt revolvable along a closed loopwherein a tensed moving casting belt travels in a downstream directionalong a mold space from an entrance into the mold space to an exittherefrom and returns from the exit to the entrance along a returnportion of the closed loop, said return portion of the closed loop beingpositioned away from the mold space, said air-pillow apparatuscomprising: a multiplicity of stationary elements; said stationaryelements having working surfaces defining a cylindrically shaped pathextending from said return portion of the closed loop toward theentrance into the mold space for guiding a moving casting belt alongsaid cylindrically shaped path with a cylindrically curved moving innersurface of a moving casting belt being adjacent to said workingsurfaces; and a source of pressurized air for feeding pressurizedbelt-levitating air to said stationary elements for pressing outwardlyaway from the air-pillow apparatus against a cylindrically curved movinginner surface of a moving casting belt for carrying at least about 90%of an overall downstream-directed component of force exertable upon theair-pillow apparatus by a tensed revolving casting belt.
 46. Air-pillowapparatus claimed in claim 45, further comprising: an air-pillow shellhaving a convex, generally cylindrical exterior and having an interior;said multiplicity of stationary elements being on said exterior; theair-pillow apparatus including walls secured to the air-pillow shellsenclosing a plenum chamber adjacent to said interior of the air-pillowshell; the air-pillow apparatus including members for mounting theair-pillow apparatus in a continuous casting machine near the entranceinto the mold space; said air-pillow shell having at least one passagetherethrough from the plenum chamber to said exterior; and said sourceof pressurized air is said plenum chamber in association with said atleast one passage through said air-pillow shell.
 47. Air-pillowapparatus claimed in claim 46, in which: said pressurizedbelt-levitating air pressing outwardly against a cylindrically curvedmoving inner surface of a moving casting belt exerts a force componentin an upstream direction on a moving casting belt which is about 250newtons per millimeter of belt width; and said force component in anupstream direction results in a tensile stress in a moving casting beltof about 10,000 newtons per square centimeter of cross section of themoving casting belt, which is a tensile stress approximating a customarytensile stress previously used in such a continuous casting machine. 48.Air-pillow apparatus claimed in claim 46 wherein a casting belt has apredetermined thickness, in which: said stationary elements on saidexterior air-pillow shell define isolated regions among them; saidisolated regions among the stationary elements when said air-pillowshell is enwrapped by a moving casting belt become isolatedbelt-levitating chambers positioned below the working surfaces of saidstationary elements; said isolated belt-levitating chambers have awidth, measured in a direction transverse to a moving casting belt,which is less than about 150 times said predetermined thickness of themoving casting belt; said air-pillow shell has a plurality of passagestherethrough; said passages communicate individually with said isolatedbelt-levitating chambers; and said passages fixedly throttle pressurizedair flowing therethrough from the plenum chamber to said stationaryelements for providing said pressurized belt-levitating air. 49.Air-pillow apparatus claimed in claim 45, further comprising: astationary support having a convex exterior; said stationary elementsbeing on said convex exterior; said working surfaces of said stationaryelements defining a cylindrically shaped path; said cylindrically shapedpath having a constant radius R1 along a major circumferential portionof said cylindrically shaped path commencing near said return portion ofsaid loop; and said air-pillow apparatus being configured for defining aminor circumferential portion of said cylindrically shaped path having avarying radius R+progressively increasing along said minorcircumferential portion of said cylindrically shaped path in a directiontoward said entrance for progressively reducing curvature of said minorcircumferential portion of said cylindrically shaped path in a directiontherealong toward said entrance; thereby progressively reducing flexuralstress in a casting belt moving along said minor portion of saidcylindrically shaped path toward said entrance.
 50. Air-pillow apparatusclaimed in claim 45, further comprising: a support having a convexexterior of generally cylindrical shape; said multiplicity of stationaryelements being on said convex exterior; said stationary elementsprotruding above said convex exterior defining isolated depressionsamong said stationary elements; said working surfaces of said stationaryelements being at a height “h” above said convex exterior; said height“h” being in a range between about 25 microns and about 2.5 millimeters;said source of pressurized air comprising passages communicatingindividually with said isolated depressions; said passages individuallyfixedly-throttling pressurized air feeding individually into saidisolated depressions for providing pressurized belt-levitating air insaid isolated depressions; and a cylindrically curved moving innersurface of such a casting belt moving along said cylindrically shapedpath being in adjacent relationship with respect to said workingsurfaces and in cooperation with said working surfaces throttlingleakage of pressurized belt-levitating air from said isolateddepressions; whereby screeching noises are substantially avoided. 51.Air-throttling apparatus claimed in claim 50, further comprising: saidworking surfaces being suitable durable, wear-resistant, slipperymaterial.
 52. Air-throttling apparatus claimed in claim 50, furthercomprising: said convex exterior having grooves therein; and saidmultiplicity of stationary elements being formed of suitable, durable,wear-resistant slippery material mounted in said grooves in snug fittingrelationship therein and protruding above said convex exterior to saidheight “h”.
 53. Air-pillow apparatus claimed in claim 46, in which: saidstationary elements on said convex exterior of said air-pillow shellcomprise an array of elevated air-throttling, belt-levitating plateaushaving thereamong a complementary array of depressed regions which areair-exhaust channels; said working surfaces are outer surfaces of saidbelt-levitating plateaus; said air-pillow shell has a plurality ofpassages therethrough individually terminating at centers of saidworking surfaces of said belt-levitating plateaus; and said passagesfixedly throttle pressurized air flowing therethrough from the plenumchamber to the centers of said working surfaces of said belt-levitatingplateaus.
 54. Air-pillow apparatus claimed in claim 53, furthercomprising: an elongate, durable, wear-resistant, perimetralair-throttling barrier extending around said array of belt levitatingplateaus and also around said array of exhaust channels on the convexexterior of said air-pillow shell; and said perimetral air-throttlingbarrier restricting escape of pressurized belt-levitating air from saidexhaust channels.
 55. Air-pillow apparatus claimed in claim 53, inwhich: said perimetral air-throttling barrier has an outwardly facingsurface with fine grooves in said surface; and said fine groovesdistribute escaping pressurized belt-levitating air over much of thesurface of said perimetral air-throttling barrier.
 56. Air-pillowapparatus claimed in claim 46, in which: said stationary elements onsaid convex exterior of said air-pillow shell comprise an array ofprotruding air-throttling barriers having thereamong a complementaryarray of depressions; said air-pillow shell has a plurality of passagestherethrough individually terminating at centers of said depressions;and said passages fixedly throttle pressurized air flowing therethroughfrom the plenum chamber to the centers of said depressions. 57.Air-pillow apparatus claimed in claim 56, further comprising: anelongate perimetral air-throttling barrier extending around said arrayof protruding air-throttling barriers and also around said array ofdepressions on the convex exterior of said air-pillow shell; and saidperimetral air-throttling barrier restricting escape of pressurizedbelt-levitating air from said depressions.
 58. Air-pillow apparatusclaimed in claim 57, in which: said perimetral air-throttling barrierhas an outwardly facing surface with fine grooves in said surface; andsaid fine grooves distribute escaping pressurized belt-levitating airover much of the surface of said perimetral air-throttling barrier. 59.A method for guiding travel of a revolving, flexible, heat-conductivecasting belt in a continuous casting machine for continuous casting ofmetal, said method guiding travel of the revolving casting belt towardan entrance into a mold space in the machine comprising steps of:providing a multiplicity of stationary elements having spacedbelt-supporting, belt-guiding, belt-path-defining working surfaces;positioning said stationary elements with their working surfaces beinglocated on a geometric sector of a convex cylinder with said workingsurfaces facing outwardly relative to said convex cylinder; positioningsuch a flexible casting belt with its inner surface facing said workingsurfaces; applying tension to the positioned casting belt for pullingthe inner surface of the casting belt against said working surfaces forconforming the inner surface of the positioned, tensioned, casting beltwith said geometric sector of the convex cylinder; feeding pressurizedair through at least one throttling passage for applying pressurized airin belt-levitating contact with the inner surface of the positioned,tensioned, and conforming casting belt for pressing the positioned,tensioned, and conforming casting belt outwardly relative to said convexcylinder for reducing force of the inner surface of the positioned,tensioned, conforming and levitated casting belt against said workingsurfaces in readiness for revolving the casting belt; and revolving thepositioned, tensioned, conforming and levitated casting belt for guidingtravel of the revolving casting belt toward the entrance into the moldspace.
 60. The method claimed in claim 59, in which: said pressurizedair in belt-levitating contact with the inner surface of the positioned,tensioned, conforming and levitated casting belt reduces force of saidinner surface against said working surfaces by at least about 90% butnot exceeding 100% of said force prior to said feeding of pressurizedair.
 61. The method claimed in claim 60, including steps of: allowingescape to ambient of pressurized air in belt-levitating contact with themoving inner surface of the positioned, tensioned, conforming andlevitated casting belt; and semi-sealing said escape to ambient of saidpressurized air.
 62. The method claimed in claim 60, including steps of:allowing escape to ambient of pressurized air in belt-levitating contactwith the moving inner surface of the positioned, tensioned, conformingand levitated casting belt; said escape to ambient occurring at aperimeter of said geometric sector of the convex cylinder; andsemi-sealing said perimeter for restricting said escape to ambient ofpressurized air.
 63. The method claimed in claim 59, including the stepsof: reducing curvature of the convex cylinder along a minor portion ofsaid geometric sector; said minor portion of said geometric sector beingnearer the entrance into the mold space than a remainder of saidgeometric sector; and said reducing curvature progressively reducescurvature of the convex cylinder in a direction of guiding travel of therevolving casting belt toward the entrance into the mold space.
 64. Themethod claimed in claim 59, including a step of: applying dry preheatingto the moving, positioned, tensioned, conforming and levitated castingbelt in proximity to said convex cylinder.
 65. The method claimed inclaim 64, in which: said dry preheating is radiant heating.
 66. Themethod claimed in claim 65, in which: said dry preheating results inheating the moving, positioned, tensioned, conforming and levitatedcasting belt to an elevated temperature in the range of about 80° C. toabout 150° C. in an area of the moving casting belt just outside of theentrance into the mold space.
 67. The method claimed in claim 59,including a step of: adjusting the pressure of pressurized air feedingthrough said at least one throttling passage for providing pressurizedair in belt-levitating contact with the inner surface of the positioned,tensioned, conforming and levitated casting belt at an adjusted pressurefor pressing outwardly at more than at least about 90% but not exceeding100% of that adjusted pressure which would lift the positioned,tensioned, conforming and levitated casting belt free from contact withsaid working surfaces.
 68. The method claimed in claim 59, includingsteps of: arranging said multiplicity of stationary elements fordefining a plurality of regions thereamong which are isolated fromnearby regions by stationary elements positioned between neighboringregions; providing said isolated regions with bottom surfaces which arepositioned inwardly relative to said convex cylinder for being depressedbelow said working surfaces; and feeding pressurized air through aplurality of throttling passages communicating individually with saidisolated regions.
 69. The method claimed in claim 68, including stepsof: providing a plurality of throttling passages communicatingindividually with said isolated regions through respective centerpositions in respective bottom surfaces of the isolated regions; andfeeding pressurized air through the plurality of throttling passagesinto center positions in respective bottoms of the isolated regions. 70.The method claimed in claim 68, in which: said pressurized air inbelt-levitating contact with the inner surface of the positioned,tensioned, conforming and levitated casting belt reduces force of saidinner surface against said working surfaces by at least about 90%, butnot exceeding 100%; thereby allowing pressurized air to escape from saidisolated regions by flowing over said working surfaces.
 71. The methodclaimed in claim 70, including steps of: allowing escape to ambient ofpressurized air flowing over said working surfaces; said escape toambient occurring at a perimeter of said geometric sector of the convexcylinder; and at said perimeter restricting said escape to ambient ofpressurized air.
 72. The method claimed in claim 71, including a stepof: arranging said multiplicity of stationary elements in a grid; andsaid perimeter extends around the grid.
 73. The method claimed in claim72, in which: the grid has a generally rectangular configuration. 74.The method claimed in claim 59, including steps of: arranging saidmultiplicity of stationary elements as ridges extendingcircumferentially relative to the convex cylinder with circumferentialchannels between neighboring ridges; and feeding pressurized air throughat least one throttling passage communicating with said channels. 75.The method claimed in claim 74, including steps of: providing aplurality of throttling passages communicating individually with saidchannels; and feeding pressurized air through the plurality ofthrottling passages into the channels.
 76. A method for guiding a movingtensed, flexible, heat-conductive casting belt along a convex,cylindrically shaped path for guiding such a casting belt as it ismoving toward an entrance into a mold space of a continuous castingmachine, said method comprising steps of: mechanically defining theconvex cylindrically shaped path by positioning a multiplicity ofstationary belt-guiding elements along the convex cylindrically shapedpath; tensing a casting belt positioned along the convex cylindricallyshaped path; applying pressurized air in belt-levitating relation to aconcave, cylindrically shaped inner surface of the casting belt; andmoving the tensed, flexible, heat-conductive casting belt into theentrance while continuing applying the pressurized air inbelt-levitating relation to the concave cylindrically shaped innersurface thereof.
 77. The method claimed in claim 76, including steps of:applying pressurized air in said belt-levitating relation which has apressure level at least about 90% but not exceeding 100% of a pressurelevel which lifts the inner surface of the casting belt away fromcontact with the stationary belt-guiding elements.
 78. The methodclaimed in claim 76, including a step of: progressively reducingcurvature of the convex, cylindrically shaped path in a direction towardthe entrance into the mold space.
 79. The method claimed in claim 76,including steps of: positioning the multiplicity of stationarybelt-guiding elements in an array extending along the convex,cylindrically shaped path and defining a plurality of regions in thearray which are isolated from nearby regions in the array; providing aplurality of throttling passages communicating individually with theisolated regions; and feeding pressurized air through said throttlingpassages to the isolated regions.
 80. The method claimed in claim 76, inwhich: said isolated regions are depressions below the convexcylindrically shaped path; and feeding pressurized air through saidthrottling passages into centralized locations in the depressions. 81.The method claimed in claim 76, in which: said isolated regions areelevated plateaus whose outer surfaces are adjacent to the convex,cylindrically shaped path; providing a plurality of throttling passagescommunicating individually with centralized locations in the outersurfaces of the elevated plateaus; and feeding pressurized air throughsaid throttling passages into the centralized locations in the outersurfaces of the elevated plateaus.
 82. the method claimed in claim 79,including a step of: allowing pressurized air to escape to ambient fromthe array; and restricting escape to ambient near a perimeter of thearray.
 83. The method claimed in claim 81, including steps of: allowingpressurized air to escape to ambient from the outer surfaces of theelevated plateaus; and restricting escape to ambient at a perimeter ofthe convex, cylindrical shape.